JITLink: Add initial SystemZ Support. (#144528)

Set up initial infrastructure for SystemZ architecture support in
JITLink. It includes features like GOT and PLT handling. Relaxation of
GOT/PLT and support for TLS were intentionally left out for the moment.

Support for TLS might require info regarding moduleID. This could
further mean changes to target independent part of JITLink and library
support.

---------

Co-authored-by: anoopkg6 <anoopkg6@github.com>

Author: anoopkg6

llvm/include/llvm/ExecutionEngine/JITLink/ELF_systemz.h

@@ -0,0 +1,39 @@
+//===--- ELF_systemz.h - JIT link functions for ELF/systemz --*- C++ -*----===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+//===----------------------------------------------------------------------===//
+//
+// jit-link functions for ELF/systemz.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_EXECUTIONENGINE_JITLINK_ELF_SYSTEMZ_H
+#define LLVM_EXECUTIONENGINE_JITLINK_ELF_SYSTEMZ_H
+
+#include "llvm/ExecutionEngine/JITLink/JITLink.h"
+
+namespace llvm {
+namespace jitlink {
+
+/// Create a LinkGraph from an ELF/systemz relocatable object
+///
+/// Note: The graph does not take ownership of the underlying buffer, nor copy
+/// its contents. The caller is responsible for ensuring that the object buffer
+/// outlives the graph.
+Expected<std::unique_ptr<LinkGraph>> createLinkGraphFromELFObject_systemz(
+    MemoryBufferRef ObjectBuffer, std::shared_ptr<orc::SymbolStringPool> SSP);
+
+/// jit-link the given object buffer, which must be a ELF systemz relocatable
+/// object file.
+void link_ELF_systemz(std::unique_ptr<LinkGraph> G,
+                      std::unique_ptr<JITLinkContext> Ctx);
+
+} // end namespace jitlink
+} // end namespace llvm
+
+#endif // LLVM_EXECUTIONENGINE_JITLINK_ELF_SYSTEMZ_H